Patients with Fuchs' dystrophy have abnormalities of the endothelial cell layer and corneal stromal edema. This edema could be due to either 1) an increased leak of fluid from the anterior chamber through the endothelial cell layer into the stroma, or 2) an inadequate functioning of the endothelial cell layer that pumps fluid out of the stroma back into the anterior chamber. Human corneal buttons from deceased normals and patients with Fuchs' dystrophy will be mounted in a chamber where an automatic system can very accurately measure the fluid flows across the corneal endothelium under various experimental conditions. From these measurements the hydraulic conductivity and therefore the fluid leak as well as the rate of fluid pumped across the endothelium can each be determined. Thus, for the first time it will be possible to independently measure both the fluid leak and fluid pump rates across normal and diseased human corneal endothelium. Hence, we could unambiguously determine if Fuchs' dystrophy is an alteration in the leak or pump functions of the endothelium.